Rhabdoviruses are helical viruses and include the virus that causes rabies and vesicular stomatitis virus (VSV), a common laboratory virus. The lipid-containing envelope is embedded with glycoprotein (G) spikes. A layer of a matrix protein (M) forms a bridge between G and the nucleocapsid proteins (N). Also included in the virion are several molecules of the RNA-dependent RNA polymerase (Large or L protein) and its cofactor, the phosphoprotein (P). The genes for these proteins are arranged as shown in the viral genome.

pathogenicity ability to cause disease

Acutely transforming retroviruses, which induce tumors in a short time period of weeks to months, carry modified versions of cellular oncogenes, called viral oncogenes. Slowly transforming retroviruses also subvert cellular oncogenes, but by integrating into or near the oncogene, thereby altering its expression, a process that can take years because of the apparently random nature of retrovirus integration.

Vaccines

Many viral infections can be prevented by vaccination. Several classes of vaccines are currently in use in humans and animals. Inactivated vaccines, such as the poliovirus vaccine developed by Jonas Salk, are produced from virulent viruses that are subjected to chemical treatments that result in loss of infectivity without complete loss of antigenicity (antigenicity is the ability to produce immunity). Another approach is the use of weakened variants of a virus with reduced pathogenicity to induce a protective immune response

without disease. While vaccines are usually given before exposure to a virus, postexposure vaccines can cure some virus infections with extended incubation periods, such as rabies.

Vaccines against smallpox eradicated the illness in 1980. It is believed that it may also be possible to eliminate polio. A recombinant vaccine against hepatitis B virus is now produced in yeast. However, developing effective vaccines to some viruses, including the common cold viruses, HIV-1, herpesviruses, and HPV, is proving very difficult principally due to the existence of many variants. Public health measures, such as mosquito control programs to curb the spread of viral diseases transmitted by these vectors, and safe-sex campaigns to slow the spread of sexually transmitted diseases, can also be effective. Because viruses replicate in cells, drugs that target viruses typically also affect cell functions. These therapeutic agents must be active against the virus while having "acceptable toxicity" to the host organism. The majority of the specific antiviral drugs currently in use target viral enzymes. For example, nucleoside analogues that target viral polymerases are active against HIV and certain herpesviruses. see also Biotechnology; Cancer; Cell, Eukaryotic; DNA Polymerases; Gene Therapy; HIV; Oncogenes; Retrovirus; Transformation; Tumor Suppressor Genes; Viroids and Virusoids.

Robert F. Garry

Bibliography

Garrett, Laurie. The Coming Plague: Newly Emerging Diseases in a World out of Balance. New York: Penguin Books, 1994.

Kolata, Gina B. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It. New York: Farrar, Straus and Giroux, 1999.

Preston, Richard. The Hot Zone. New York: Random House, 1994.

Internet Resource

Sanders, David M., and Robert F. Garry. "All the Virology on the World Wide Web." <www.virology.net>.